Polishing machine

ABSTRACT

CONTROL MEANS FOR SELECTIVELY CONTROLLING THE PRESSURE BETWEEN A POLISHING HEAD AND A CONTOURED OBJECT, IN ACCORDANCE WITH THE SURFACE ZONE BEING POLISHED. THE CONTROL MEANS COMPRISE POSITION RESPONSIVE MEANS WHICH PRODUCE AN ELECTRICAL POSITION SIGNAL AS THE POLISHING HEAD TRAVERSE EACH BOUNDARY BETWEEN ADJACENT SURFACE ZONES, A SEQUENCE CONTROL CITCUIT TO WHICH THE SUCCESSION OF POSITION SIGNALS ARE FED AND WHICH DELIVERS OUTPUT SIGNALS IN SEQUENCES AS EACH POSITION SIGNAL IS RECEIVED, AND A PRESSURE CONTROLLING DEVICE WHICH ACTS TO CONTROL THE POLISHING PRESSURE SELECTIVELY IN ACCORDANCE WITH THE PREVAILING OUTPUT SIGNAL.

Feb. 16, 1971 CLAYSQN ETAL 3,562,961

POLISHING MACHINE 6 SheetsSheet 1 Filed Sept. 5. 1968 INVENTORS my W 7 ATTORNEYS Feb. 16, 1971 I CLAYSQN ETAL 3,562,961

POLISHING MACHINE Filed Sept. 5, 1968 e Sheets-Sheet An /p JOHN SMITH INVENTORS Wyn-M7, rJ/ W ATTORNEYS Feb. 16, CLAYSQN EI'AL 3,562,961

POLISHING MACHINE 6 Sheets-Sheet 8 Filed Sept. 5, 1968 A EA/w: m Huaaer 61. Am)

0/9 W0 do/w SM/r/l INVENTORS' BY W r'c7 ATTORNEYS Feb. 16, 1971 CLAYSQN EI'AL 3,562,961

POLISHING MACHINE Filed Sept. 5, 1968 6 Sheets-Sheet 4 INVENTORS ATTORNEYS Feb. 16, 1971 CLAYSQN ETAL 3,562,961

} POLISHING MACHINE Filed Sept. 5. 1968 6 Sheets-Sheet 5 INVENTOR BY W l JM ATTORNEYS nited States Patent Olfice 3,562,961 Patented Feb. 16, 1971 3,562,961 POLISHING MACHINE Kenneth Hubert Clayson, Solihull, and David John Smith, Birmingham, England, assignors to Wilmot-Breeden Limited, Birmingham, England Filed Sept. 3, 1968, Ser. No. 756,941 Int. Cl. B24b 21/00, 49/00 US. Cl. 51138 9 Claims ABSTRACT OF THE DISCLOSURE Control means for selectively controlling the pressure between a polishing head and a contoured object, in accordance with the surface zone being polished. The control means comprise position responsive means which produce an electrical position signal as the polishing head traverses each boundary between adjacent surface zones, a sequence control circuit to which the succession of position signals are fed and which delivers output signals in sequences as each position signal is received, and a pressure controlling device which acts to control the polishing pressure selectively in accordance with the prevailing output signal.

This invention relates to control equipment for a machine for polishing contoured objects such, for example, as bumper bars for motor vehicles, and to a polishing method and polishing machine utilising such equipment.

The polishing of a bumper bar is complicated by the fact that different parts of the surface of the bar require different polishing pressures if a consistent surface finish is to be obtained and if undue wear of the abrasive polishing elements is to be eliminated. One object of the present invention is to provide apparatus for automatically controlling a polishing machine such that the polishing pressure is varied to suit the particular part of the surface being polished.

According to one feature of the invention control means for selectively controlling the pressure between a polishing head and a contoured object being polished in accordance with the surface zone being polished, comprise position responsive means which produce an electrical position signal as the polishing head traverses each boundary between adjacent zones, a sequence control circuit to which the succession of position signals are fed and which delivers output signals in sequence as each position sig nal is received, and a pressure controlling device which acts to control the polishing pressure selectively in accordance with the prevailing output signal.

It will be appreciated that either the object being polished can be moved past the polishing head so that the latter traverses said zones in succession or alternatively that the object can be held stationary and the head moved. Preferably the sequence control circuit in use continuously provides an output signal the magnitude of which changes as each position signal is received.

Means in accordance with the invention are particularly applicable to the polishing of bumper bars of motor vehicles. In this case the surface of a bar may be considered as including a number of rows of zones with each row extending along the bar so that each boundary between adjacent zones is disposed transversely with respect to the longitudinal direction of the bumper bar. The bumper bar is conveniently mounted on a jig which is movable horizontally to traverse the bar in a longitudinal direction below the polishing head. A plurality of polishing heads may be provided disposed around a continuous horizontal track with the bumper jigs being movable around the track so that each bumper is engaged in turn by the polishing heads.

The position responsive means preferably comprise a row of stationary detectors respectively corresponding to the various boundaries, each detector producing an electrical impulse forming the corresponding position signal when the polishing head traverses the corresponding boundary. Each detector is conveniently in the form of a reed switch and operating magnet with a suitable air gap between these components, a magnetic shield being provided which is movable with the bumper jig and arranged to pass in turn through the air gaps of the detectors thereby actuating the latter in sequence. The number and relative positions of the detectors thus determines the number and the lengths of the zones to which different polishing pressures are selectively applied.

Alternatively, the position responsive means may comprise an encoder which produces output pulses the frequency of which is proportional to the speed of traverse of the bumper jig, and a ring counter which counts the pulses and controls rotary selector switches which are individually programmed and which produce the position signals at intervals in accordance with the number of pulses counted and the programmes. In this case some datum position of the bumper jig must be taken from which the ring counter starts to count the pulses, and this datum position is conveniently achieved by means of a single reed switch and associated operating magnet, the bumper jig again having a magnetic shield which actuates the reed switch to provide a datum signal which sets the datum position for the ring counter. After this the distance of traverse of the bumper jig from the datum position is represented by the number of pulses emitted by the encoder. The position responsive means may also comprise a logic loop which ensures that position signals are only produced during pulsing of the encoder and following the datum signal from the reed switch.

The sequence control circuit preferably employs adding or and circuit stages and a corresponding number of bistable state or latch" circuit stages connected alternately in sequence as described in US. patent application No. 756,939, filed Sept. 3, 1968, to which reference should be made for details of such a circuit arrangement.

The pressure controlling device preferably comprises a pneumatic cylinder and a series of pressure regulating valves which act to control the air pressure in the cylinder and which are selectively operated by solenoids energised by the output signals. The piston is preferably doubleacting so that the polishing head may be raised and lowered automatically.

According to another feature of the invention a method of polishing a contoured object the surface of which includes zones each of which requires its own substantially constant polishing pressure comprises the steps of producing an electrical position signal as a polishing head traverses each boundary between adjacent zones, feeding the succession of signals to a sequence control circuit which delivers output signals in a sequence, each change point of the sequence being triggered by one of the position signals, and selectively controlling the polishing pressure in accordance with the output signals.

According to a further feature of the invention, a machine for polishing a contoured object comprises a polishing head, means for supporting the object and producing relative traverse of the latter and the head during polishing, means to apply a desired polishing pressure to the head, and control means which produce a sequence of electrical position signals dependent upon the traversing position of the head and object and include a sequence control circuit to which the position signals are fed and which produces output signals which operate to control the polishing pressure.

Preferably the machine includes a plurality of polishing heads past which the object is traversed in turn. Diflerent grades of polishing may be achieved by different heads, and the heads may be angled so that different regions of the object are polished by diflerent heads.

Each head will normally be controlled by its own separate control means, and may comprise an endless abrasive band which passes around a jockey wheel which provides a flexible and resilient backing to allow the band to conform to the object. The jockey wheel may be mounted on a swinging link controlled by a pneumatic cylinder to provide the polishing pressure, and to raise the head from the object, and each head may include its own driving motor.

The invention will now be further described with reference to the accompanying drawings which show, by way of example, two forms of polishing machine in accordance with the invention for polishing bumper bars of motor vehicles. In the drawings:

FIG. 1 is a general perspective and somewhat diagrammatic view of one complete machine,

FIG. 2 is a view, on an enlarged scale, of one of a plurality of polishing stations of the machine,

FIG. 3 is a view of a bumper bar illustrating a row of polishing zones,

FIG. 4 is a view of a detector of the control means associated with one polishing station,

FIG. 5 is a block circuit diagram of the control means associated with one of the polishing stations,

FIG. 6 is a diagrammatic view of the other machine, illustrative of modified control means, and

FIG. 7 is a diagram in logic form of the modification of FIG. 6.

Referring to FIG. 1, the polishing machine comprises a plurality of polishing stations 2a, 2b, 2c, and 2d longitudinally spaced along two straight sides 3 of the continuous horizontal track 4 around which a number of platens 5 are movable in a clockwise direction when viewed from above the polishing machine. Each platen 5 carries a jig 6 on which can be mounted a bumper bar 7 so that the bars are movable around the track 4 and past the polishing stations 2a, 2b, 2c in turn. The polishing stations 2a, 2b, 2c respectively include polishing heads 8a, 8b, 8c which are separately mounted on stands 9a, 9b, 9c Separate control means are provided at each polishing station 2a, 2b, 2c the control means acting to selectively control the polishing pressure between the corresponding head and the bumper bars as the latter pass beneath the head. Each polishing station 2a, 2b, 2c is of identical form but for the fact that the polishing heads 8a, 8b, 8c are angled by ditferent amounts so that diiferent regions of the bars are polished by different heads. Accordingly, the operations of the machine will hereinafter be described for one polishing station 2 only.

The polishing station 2 is shown in greater detail in FIG. 2 which shows the polishing head 8 comprising an endless abrasive band 10 which passes around a jockey wheel 12 which is in the form of a laminated felt wheel to provide a flexible and resilient backing for the band 10, thus allowing the latter to conform to the contoured surface of the bumper bar 7. The abrasive band 10 also passes around an idler wheel 11 and a drive wheel (not shown) which is driven by an electric motor (not shown) embodied in the head 8. The polishing head 8. also comprises a swinging link 13 the upper end of which is pivotally mounted about a fixed point 14 and the lower end 15 of which is pivotally connected to the centre of the jockey wheel. Adjacent its lower end 15 the link 13 is connected to a double-acting piston 16 which is reciprocable in a pneumatic cylinder 17 into opposite ends 18, 19 of which air under pressure may be selectively supplied. By controlling the pressure in the end 18 of the cylinder 17 the polishing pressure is controlled.

The control means provided at the polishing station 2 comprise position responsive means which embody a number of longitudinally spaced detectors arranged beside the track 4 at the polishing station 2. The surface of each bumper bar 7 may be considered as including a number of rows of zones with each row extending along the bar 7 so that each boundary between adjacent zones is disposed transversely with respect to the longitudinal direction of the bumper bar 7. FIG. 3 illustrates a corresponding row of five zones designated 22 to 26 at the polishing station 2, and the bumper bar 7 passes through these zones in turn. The bumper bar 7 is illustrated centrally within the five zones 22 to 26, and the zones 23 to 25 can be considered as representative of three zones of the bumper bar 7 which are to be polished. The end zones 22 and 26 represent distances through which the bumper bar 7 moves during lowering and raising of the head 2 respectively. In this case six detectors 27 to 32 are spaced along the track at the polishing station 2, and correspond with the six boundaries of the five zones 22 to 26. Each detector (shown in detail in FIG. 4) is in the form of a yoke with horizontally extending limbs 34, 35 disposed one above the other, with the upper limbs 34, housing a reed switch 36 and the lower limb 35 incorporating an operating magnet 37. The yoke form of each detector 27 to 32 provides an air gap between the reed switch 36 and the operating magnet 37 so that the contacts of the reed switch 36 are normally maintained closed under the influence of the operating magnet 37.

A piece of steel strip fixed to each bumper jig 6 forms a magnetic shield 38 which, during traverse of the jig 6 below the polishing head 2, passes in turn through the air gaps in the detectors thereby shielding the reed switch 36 from the magnetic influence of the operating magnet 37. When this occurs the contacts of the reed switch 36 open, providing an electrical impulse which forms a position signal. By suitably positioning the detectors 27 to 32, a position signal is emitted from one of the detectors 27 to 32 each time the polishing head 8 traverses the corre sponding boundary.

Lead wires 39 to 44 respectively connect the detectors 27 to 32 to a sequence control circuit 46 which provides output signals in sequence as the position signals are received. The circuit 46 comprises a plurality of and and latch circuit stages arranged alternately in sequence as described in US. patent application No. 756,939, filed Sept. 3, 1968, to which reference should be made for a detailed description of the operation of the circuit 46.

The output signals from the circuit 46 are fed to a bank of lights 47 which indicate the particular zone of the surface of the bar 7 being polished and to a bank of switches 50 which provide manual control when required. The output signals are also fed to a pressure controlling device 48 which acts to selectively control the polishing pressure and to raise and lower the polishing head 8. The pressure controlling device 48 is shown in FIG. 5 and comprises five pressure regulating valves, namely a five-way valve 51 and four three-way valves 52 to 55. Associated with the valves 51 and 55 are pressure regulators 56 to 60, pressure gauges 62 to 66 and operating solenoids 67 to 71 respectively, the solenoids selectively operating the valves 51 to 55 and being energised by the output signals from the sequence control circuit 46.

An air pressure line 72 supplies each pressure regulator 56 to 60, outlets of the pressure regulators respectively communicating with the pressure gauges 62 to 66 and also with one inlet of the corresponding valves 51 to 55. One outlet of the five-way valve 51 communicates with the end 17 of the cylinder 19 through a' pneumatic line 73 and an outlet of the last three-way valve 55 communicates with the end 18 of the cylinder 19 by means of a further pneumatic line 74. A valve member of each of the valves 51 to 55 is movable, under the control of the corresponding solenoid 67 to 71, from a position providing a flow path designated a in FIG. 5 to a position providing a flow path designated b in this figure.

The operation of the control means during a complete polishing stroke in which a complete row of zones 23 to 25 is polished will now be described.

Initially all the valves are in position a and the head 8 is in the raised position, air under pressure being supplied through the pneumatic line 73 to the end 17 of the cylinder 19. The movement of the bumper 7 (and the shield 38) is from left to right as viewed in FIGS. 2 and 5 and just before the leading end of the bumper bar 7 reaches the polishing head 8, the shield 38 actuates the detector 27 thereby causing the output signals of the control circuit 46 to sequence one step. This causes the first solenoid 67 to be actuated thereby changing over the fiveway valve 51 from position a to position b. Air under pressure now passes through the valves 51 to 55 in turn and through the pneumatic line 74 to the end 18 of the cylinder 17 so that the piston 16 is moved inwardly thereby lowering the head 8 while the bar 7 moves through a distance represented by the zone 22.

During lowering of the head 8, the shield 38 actuates the next detector 28 causing a further step in the sequence of the output signals from the circuit 46. This further step actuates the solenoid 68 to change over the valve 52 from position a to position b so that the pressure in the end 18 of the cylinder 17 is governed by the pressure regulator 57. The head 2 thus polishes the zone 23 with a pressure which is determined by the setting of the pressure regulator 57. Further movement of the shield 38 actuates the detector 29 which causes the control circuit 46 to sequence a further step thus actuating the solenoid 69 so that the pressure regulator 58 becomes operative to control the air pressure in the cylinder 17 during polishing of zone 24. On actuation of the solenoid 69 the valve 52 reverts to position a.

Similar sequencing of the output signals occurs until the shield 38 reaches the detector 31 which actuates the solenoid 71 to change over valve 55 from position a to position b. Actuation of the detector 32 causes the pressure controlling device 48 to reset so that the head is raised, the cycle then repeating itself when a further bumper bar 7 approaches the polishing head 2. Thus, the polishing pressure is selectively controlled by means of the pressure regulators 56 to 60 which govern the magnitude of the air pressure in the end 18 of the cylinder 17 in accordance with the zone being polished.

In the modification of the position responsive means shown in FIGS. 6 and 7 a single detector 80 is provided with a shaft encoder 81 which is mechanically coupled to a conveyor 82 on which the bumper bars 7 are mounted. The encoder 81 produces pulses the frequency of which is proportional to the speed of traverse of the bumper bar 7 beneath the polishing head 2.

The detector 80 is again in the form of a reed switch and associated magnet and in this case the magnetic shield 83 is fixed to the conveyor 82. The pulses from the encoder 81 are fed to the circuit shown in FIG. 7 which includes a ring counter 84 and six rotary selector switches 85 which are individually programmed to produce the position signals after the appropriate number of pulses has been counted by the ring counter 84. In order to achieve this the count in the ring counter 84 is compared with the numbers which are preset by the programmes on the selector switches 85. When parity is obtained between the count on the ring counter 84 and one of the selector switches 85, this switch produces a position signal which is fed to the sequence control circuit 46 shown in FIG. 7.

The circuit of FIG. 7 comprises a logic loop 86 which ensures that position signals are only supplied to the sequence control circuit 46 during pulsing of the encoder 81 and following receipt of a datum signal from the detector 80. This is achieved by means of a latch stage 87 and and stages 88. The latch stage is bistable and may occupy an inoperative state in which no output is supplied to the and stages 88 or a triggered state in which such an output is supplied to the and stage 88. Thus, when the datum signal is received from the detector 80 the latch stage 87 resets the ring counter 84 by means of the line 90 and produces a signal at a further and stage 93 after which pulses from the encoder 81 step on the ring counter 84. Since the latch stage 87 is now triggered the and stages 88 relay the position signals. In the event of mains failure and subsequent restoration an automatic reset device 92 is provided which supplies an or stage 91 which is connected to the latch stage 87.

A machine in accordance with the invention has the particular advantages that certain surface zones of a contoured object may be given special polishing treatment in order to remove surface defects, and that surfaces including projections or cavities may be polished by arranging for the head to rise over such obstacles or to ride over them at reduced pressure. Furthermore, the provision of selectively controlled polishing pressures for the head increases the utilisation time for the head so reducing the time during which the head is idle. The use of reed switches eliminates the need for sliding electrical contacts which are subject to wear and the operation of which can be unreliable due to misalignment or the presence of conducting dust.

We claim:

1. A machine for polishing a contoured object, comprising a polishing head, a support for the object, traversing means producing relative movement between said head and said object during polishing, a pressure controlling device to apply a range of polishing pressures between said head and a surface of said object, and control means for selectively controlling the polishing pressure in accordance with the surface zone being polished, said control means including position responsive means which produces an electrical position signal as the polishing head traverses each boundary between adjacent surface zones, and a sequence control circuit coupled to receive position signals in succession from said position responsive means and producing output signals operative upon the pressure controlling device to determine successive polishing pressures.

2. A machine according to claim 1, wherein the sequence control circuit in use continuously produces an output signal the magnitude of which changes as each position signal is received.

3. A machine according to claim 1, wherein the position responsive means comprise a row of stationary detectors respectively corresponding to the various zone boundaries.

4. A machine according to claim 3, wherein each detector is in the form of a reed switch and an operating magnet separated from the switch by an air gap, a magnetic shield being provided which is movable with the object being polished as the latter is traversed past the polishing head so that the shield passes in turn through the air gaps of the detectors thereby actuating the latter in sequence.

5. A machine according to claim 1, wherein the position responsive means comprise an encoder which produces output pulses the frequency of which is proportional to the speed of traverse of the object relative to the polishing head, and a ring counter which counts the pulses and controls rotary selector switches which are individually programmed and produce the position signals.

6. A machine according to claim 5, wherein a datum position from which the ring counter starts to count is provided by a signal produced by a reed switch and associated operating magnet when a magnetic shield, movable with the object as the latter moves up to the polishing head, enters an air gap between the switch and magnet.

7. A machine according to claim 6, wherein the position responsive means also comprise a logic loop which ensures that position signals are only produced during pulsing of the encoder and following receipt of a datum signal from the reed switch.

8. A machine according to claim 1, which the pressure controlling device comprises a pneumatic actuator and a series of pressure regulating valves which act to control the air pressure in the actuator and which are selectively 7 8 rendered operative by solenoids energised by the sequence 3,178,860 4/ 1965 Clyne Q. 51- 138 control circuit. 3,237,348 3/ 1966 Block 5174 '9. A machine according to claim 8, wherein the actua- 3,271,909 9/ 1966 Rutt et al 5176X tor is double-acting and operates to both raise and lower 3,295,261 1/1967 Murray 5176X the polishing head automatically. 5 3,376,672 4/ 1968 Schmidt 51-76 3,394,501 7/1968 Carlson et al 51-138 References Cited UNITED STATES PATENTS 2,073,786 3/1937 Doutt 5138 CL 2,108,193 2/1938 Brackett 51-74 10 51 165 LESTER M. SWINGLE, Primary Examiner 

